The present invention relates to a substrate and a liquid crystal display (LCD) device, and particularly relates to a wire structure of the same and a method for fabricating the same.
Recently liquid crystal display (LCD) devices having greater display capacities and higher image quality have been demanded, and LCD devices of active matrix driving type in which switching elements are respectively provided for pixels constituting display screens have been developed in response to the foregoing demand. For example, as the foregoing switching elements, thin film transistor (TFT) elements and metal-insulator-metal (MIM) elements have been turned to practical use.
FIG. 9 illustrates a structure of a liquid crystal cell using MIM elements.
Generally, the liquid crystal cell has a structure consisting of an element substrate 1 and a counter substrate 2 that are made to adhere to each other with a sealing material 16, and liquid crystal is sealed inside to the sealing material 16. Furthermore, to arrange a desired optical system, an optical film such as, for example, a polarizing plate 17 is applied on at least a surface side of the liquid crystal cell.
Furthermore, as shown in FIG. 10, each pixel on the element substrate 1 is composed of a signal wire 3, a MIM element 4, and a pixel electrode 6. The MIM element 4 is composed of a lower electrode 3a, a thin insulator 9 (see FIG. 11(b)) formed so as to cover the lower electrode 3a, and an upper electrode 5, so as to be formed at an intersection of the lower electrode 3a and th e upper electrode 5.
As shown in FIG. 9, to apply signals to the pixels, element-side terminal electrodes 10 are provided on the same surface of the element substrate 1 on that the signal wires 3 (see FIG. 11(a)) are provided, and connection wires 7 are formed so as to connect the signal wires 3 with the element-side terminal electrodes 10. On the counter substrate 2, there are provided counter-side electrodes 14 as well as counter-side terminal electrodes 12 and connection wires 13 for applying signals to the counter-side electrodes 14.
Display of images is carried out by connecting driving-use circuit members 11 and 15 with the element-side terminal electrodes 10 on the element substrate 1 and the counter-side terminal electrodes 12 on the counter substrate 2, and by applying predetermined signals thereto.
The following description will explain a common method for fabricating the element substrate 1 using such MIM elements 4, while referring to FIGS. 11(a) through 11(d).
First of all, as shown in FIG. 11(a), a first conductive material is laminated on a glass substrate by sputtering or the like, and it is patterned to predetermined shapes by photolithography, so that the signal wires 3, the lower electrodes 3a, the connection wires 7, and the element-side terminals 8 should be formed.
Next, as shown in FIG. 11(b), thin insulators 9 are provided at least on surfaces of the lower electrodes 3a. Generally, to form the insulators 9, a method of soaking the element substrate 1 into electrolytic liquid and applying a voltage thereto, that is, so-called anodization, is applied. If upon the anodization the insulators 9 are provided over the element-side terminal electrodes 10, it should be inconvenient, since conduction will not be provided between the element-side terminal electrodes 10 and the circuit member 11 at later stages. Therefore, the following process is applied: the element-side terminal electrodes 8 are covered with protective films such as resin beforehand, and anodization is applied thereto in this state, then, the protective films are removed.
Further, as shown in FIG. 11(c), a second conductive material that will be later formed into the upper electrodes 5 composing the MIM elements 4 is laminated by sputtering or-the like, and thereafter it is patterned to predetermined shapes by photolithography.
Finally, as shown in FIG. 11(d), a third conductive material that will be later formed into the pixel electrodes 6 is laminated by sputtering or the like, and thereafter it is patterned to predetermined shapes by photolithography. Incidentally, to ensure reliability of electric connection between the circuit member 11 and the element-side terminals 8, the element-side terminal electrodes 10 are sometimes provided to the element-side terminals 8.
FIGS. 12(a) through 12(d) illustrates another method for fabricating the element substrate 1.
First, as shown in FIG. 12(a), the first conductive material is laminated on a glass substrate by sputtering or the like, and it is patterned to predetermined shapes by photolithography, so that the signal wires 3, the lower electrodes 3a, the connection wires 7, and the element-side terminals 8 should be formed.
Next, as shown in FIG. 12(b), the thin insulators 9 are provided on an entirety of surfaces of the first conductive material by anodization, and through holes 18 are formed by patterning the insulators 9 covering surface of the element-side terminals 8, so that the first conductive material should be exposed through the through holes 18.
Further, as shown in FIG. 12(c), the second conductive material that will be later formed into the upper electrodes 5 composing the MIM elements 4 is laminated by sputtering or the like, and thereafter it is patterned to predetermined shapes by photolithography.
Finally, as shown in FIG. 12(d), the third conductive material that will be later formed into the pixel electrodes 6 is laminated by sputtering or the like, and thereafter, it is patterned to predetermined shapes by photolithography. Incidentally, to ensure reliability of electric connection between the circuit member 11 and the element-side terminals 8, the element-side terminal electrodes 10 are sometimes provided to the element-side terminals 8, like the aforementioned fabrication method.
By either of the foregoing fabrication methods, the insulators 9 that are uniform can be formed since the substrate is not soiled with resin and the like before anodization. Therefore, the foregoing fabrication methods can provide an advantage that the MIM elements 4 having less differences in characteristics can be obtained.
On the other hand, the counter substrate 2 is more easily formed than the element substrate 1 is. For example, after an electrode material is laminated on a glass substrate by sputtering or the like, the counter-side terminal electrodes 12, the connection wires 13, and the counter-side electrodes 14 are simultaneously formed by patterning, whereby the counter substrate 2 is obtained.
Furthermore, the counter substrate 2 occasion ally does not require so fine wiring processing as the element substrate 1 does, and in such a case, patterning of the counter-side terminal electrodes 12, the connection wires 13, and the counter-side electrodes 14 is realized by sputtering of an electrode material with use of deposition masks.
On electrode film surfaces of display areas of the element substrate 1 and the counter substrate 2 thus formed, an alignment film (not shown) is provided. After applying a rubbing operation thereto, the substrates 1 and 2 are combined in a manner such that the electrodes face each other, and is made to adhere to each other with a sealing material 16. Through an opening (not shown) provided at a certain position, liquid crystal is injected by vacuum injection or the like, and is sealed. Thereafter, an optical film such as a polarizing plate 17 is applied over a display surface of the liquid crystal cell, and the circuit member 11 is attached. Thus, an LCD device is completed.
Generally, a liquid crystal cell is fabricated by fabricating a large-size mother glass equivalent to a plurality of liquid crystal cells and by cutting out each liquid crystal cell from the mother glass. Therefore, in the case where the liquid crystal cells have display regions of equal areas to each other, frame regions that are non-display regions and where the element-side terminal electrodes 10 are provided should be made narrower so that. the number of liquid crystal cells obtained from one mother glass could be increased, whereby manufacturing costs can be reduced. It is also demanded to decrease the pitch of terminals of the element-side terminal electrodes 10 as the circuit members are made smaller for reduction of costs.
However, decrease of each space between adjacent terminals and narrowing of the frame regions may make it difficult to form the connection wires. This problem is explained below with reference to FIGS. 13 through 15.
Note that the polarizing plate 17 is not shown in FIGS. 13 through 15.
For example, as shown in FIG. 13, the spaces between connection wires 7 become wide in the case where the pitch of the element-side terminal electrodes 10 is increased. Therefore, in this case hardly occurs the short-circuiting between the connection wires 7 due to remnants of a film of a material of the connection wires 7 after patterning the film to the connection wires 7. Besides, since the lengths of the connection wires 7 do not substantially differ, the connection wires 7 undergo only small differences in resistances.
As shown in FIG. 14, however, spaces between the connection wires 7 are narrowed as the terminal pitch is decreased, thereby possibly causing the short-circuiting of the connection wires 7 due to remnants of the film after patterning. Moreover, since the lengths of the connection wires 7 greatly differ, the differences between resistances of the connection wires 7 increase. In the case where the resistances of the connection wires 7 differ greatly, voltage values applied to the signal wires 3 come to differ from each other even in the case where the same voltage is applied to the element-side terminal electrodes 10, thereby causing shades of display at the pixels to deviate from appropriate ones.
In this case, for example, as means to solve the foregoing problem, the connection wires 7 may be broadened in proportion to the lengths thereof, as shown in FIG. 11(a), so that they should have uniform resistances. This however causes the spaces between long ones among the connection wires 7 that are broadened in width for adjustment of their resistances to have further narrower spaces therebetween, thereby increasing possibility of occurrence of short-circuiting. On the other hand, if short ones among the connection wires 7 are narrowed in width for adjustment of their resistances, possibility of occurrence of wire-breaking increases, and this is also inconvenient.
As shown in FIG. 15, even though the terminal pitch is not decreased, the lengths of the connection wires 7 come to greatly differ in the case where the liquid crystal cell is made smaller in size, and an identical problem to that above described occurs.
Such a problem as non-uniformity of resistances of the connection wires 7 can be solved by using a low-resistance material such as aluminum (resistivity: 4 xcexcxcexa9xc2x7cm). This is because use of a low-resistance material not only makes the resistances of the connection wires 7 smaller, but also decrease differences of the resistances of the connection wires 7 due to the differences in their lengths and shapes.
However, the wire material used for forming the connection wires 7 is also the material used for forming the lower electrodes 3a, and therefore, wire materials that can be used for forming the connection wires 7 are limited, to obtain MIM elements 4 having excellent element characteristics. A wire material now put into practical use is only Ta that has a relatively high resistivity (resistivity: about 25 to 20 xcexcxcexa9xc2x7cm). Therefore, a material with a low resistivity such as Al (resistivity: 4 xcexcxcexa9xc2x7cm) cannot be used for forming the connection wires 7.
Furthermore, broadening the widths of the connection wires 7 to make the resistances of the connection wires 7 uniform not only causes the possibility of short-circuiting to increase, but also occasionally spoils the appearance of the liquid crystal cell. For instance, in a monochrome liquid crystal cell having no color filters and adopting the MIM elements 4 using a light-blocking wire material, regions for the connection wires 7 adjoin pixel regions for the pixel electrodes 6, and directly enter the user""s field of vision. Therefore, the wire patterns of the connection wires 7 become awkwardly remarkable.
Thus, the dimensions of the connection wires 7 are limited according to requirements for making the resistances of the wires uniform. On the other hand required is right wiring dimensions that do not cause defect patterns and, in some cases, that do not cause appearance to be spoiled.
In order not to cause wire-breaking of the connection wires 7, a wire width of approximately 10 xcexcm is required though it depends on performances of manufacturing lines of the liquid crystal cells. Besides, the wires with a wire width of approximately 30 xcexcm may cause the user to feel uncomfortable though it may depend on individuals. In the liquid crystal cells in these days, a ratio between the length of long ones and the length of short ones among the connection wires 7 not rarely becomes approximately 3:1. Therefore, with the foregoing method in which the width and length of the connection wires 7 are simply adjusted, it is difficult to design the liquid crystal cell so as to make the resistances uniform.
An object of the present invention is to provide a wire structure, a method for fabricating a substrate, a LCD device, and a method for fabricating the same that can provide uniform resistances of connection wires while avoiding short-circuiting and wire-breaking.
To achieve the foregoing object, a wire structure of the present invention is a wire structure comprising a plurality of connection wires that connect a plurality of signal wires with a plurality of terminals on a substrate, respectively, wherein (i) each of the connection wires has a plurality of connection parts having different cross-sectional structures, respectively, so that the connection parts should have different resistances, and (ii) the plurality of connection parts are arranged so that all the connection wires should have substantially uniform resistances.
The foregoing invention ensures that signal voltages fed through terminals on a substrate are applied to desired signal wires, respectively, through connection wires.
Generally, distances from terminals on a substrate to corresponding signal wires differ from each other, thereby causing resistances of connection wires connecting the terminals with the signal wires to differ from each other. Such differences in resistances lead to irregularities in signal voltages applied to the signal wires that make the signal voltages vary from desired values, thereby causing the reliability to lower. To overcome this problem, devised is an arrangement in which widths of the connection wires are varied so as to make the resistances of the connection wires uniform. However, this leads to the following problem, when the terminal pitch decreases (spaces between terminals become narrower) as circuit integration is further promoted. Namely, it is necessary to make widths of the connection wires different so as to make all the connection wires have uniform resistances, but in the case where the connection wires are long, they are made broader in width, thereby causing short-circuiting to easily occur between adjacent ones of the same. On the other hand, in the case where the connection wires are short, they are made narrower in width, thereby causing wire-breaking to easily occur.
Conversely, according to the foregoing invention, the connection parts are made to have different cross-sectional structures in the thickness direction. In other words, it is possible to make the connection parts have different resistances per unit length in accordance with their cross-sectional structures in the thickness direction, respectively. Thus, by causing the connection parts to have different resistances, respectively, adjustment to make the resistances of the connection wires uniform is enabled. In other words, not by making the widths of the connection wires different, but by making the cross-sectional structures in the thickness direction different, the connection wires are made to have widths in an appropriate range. Consequently, the short-circuiting and wire-breaking occurring to connection wires due to non-uniform widths of the connection wires in the conventional cases can be surely prevented. The cross-sectional structures in the thickness direction can be changed by, for example, changing the thickness of the conductive material layer, or making the layer in a multi-layer structure made of not less than two different conductive materials.
Further, the foregoing plurality of connection parts are provided so that all the connection wires should have substantially uniform resistances. This ensures that resistances are substantially uniform at any terminals. Thus, since the terminals do not undergo differences in resistances, the signal voltages applied to the signal wires do not have irregularities, thereby ensuring that desired signal voltages can be applied to the terminals. Consequently, the reliability of circuit operations is enhanced.
Furthermore, when the predetermined widths of the foregoing plurality of connection parts are equal to each other, the short-circuiting between the connection wires hardly occur as compared with the conventional schemes: in the conventional schemes, the resistances are made substantially uniform between the connection wires by adjusting the wire widths of the connection wires individually; in the present invention, spaces between the connection wires are kept uniform even in the case where the connection wires are laid in a complicated arrangement.
Therefore, the resistances of the connection wires can be easily made uniform, thereby enabling to narrow spaces between the terminals. As a result, circuit members small in size and inexpensive can be used, thereby enabling to lower costs. Furthermore, a higher degree of freedom is allowed in layout of connection wires, and the number of the foregoing substrates obtained from one mother board increases. Consequently, the manufacturing costs as a whole can be surely lowered.